1. Field of the Invention
The present invention relates gyrocompasses. More particularly, this invention pertains to a gyrocompass having at least one electrically driven gyro in a gas-tight capsule mounted to float in an electrically conducting liquid inside a compass casing and supplied from an external current source through the capsule wall.
2. Description of the Prior Art
It has long been known to install one, two or more mutually mechanically-coupled, electrically-operated gyros inside a generally spherical casing or capsule to ensure storage largely free from environmental influences and exhibiting low loss and low friction. While it would be desirable to evacuate the capsule to reduce frictional losses, it is required to fill the capsule with a gas which is as light as possible, and preferably inert (e.g., with hydrogen or helium) to dissipate the heat losses unavoidably produced by the gyro drive. The capsule must, therefore, be absolutely airtight over very long periods of time (i.e., from several years to decades). Appropriate cable bushings are necessary for supplying the gyro with current, placing extreme tightness specifications on the bushings.
As it is impossible to produce a more-or-less spherical one-piece capsule, it is known to produce the capsule holding the gyro from two essentially-hemispherical shells (denoted below as xe2x80x9clowerxe2x80x9d and xe2x80x9cupperxe2x80x9d shells). The two shells are plugged together in the region of their free rims in an overlapping, and mutually adapted, fashion to form the desired spherical capsule. They are hermetically sealed to one another by means of a circumferential sealing packing.
It is known to produce the two shells from a conductive material. Aluminum has always been preferred due to its low specific weight. Since the capsule is mounted to float inside a conductive liquid within the compass casing (i.e., in an electrolyte), it is mandatory, for avoiding more-or-less rapid dissolution of the capsule casing, to provide a very thick adhesive, chemically neutral coating on the exterior of the casing. The smallest gaps, cracks or damage in or to the coating lead, sooner or later, to capsule leaks, particularly in the regions of the electric bushings and/or the equatorial joint. To insure tightness, particularly in the equatorial region of a joint between the lower and upper shells 1, 2 (compare FIG. 5), a preferably shrunk-on equatorial ring 11 of plastic is additionally provided at the exterior.
In order to determine the instantaneous azimuthal position of the gyro, it is, however, necessary to provide a conductive region that spans at least a sub-region of the equator (the so-called azimuthal tap) on the outside of the casing. Such region is formed in present-day gyrocompasses by, for example, a conductive, preferably gilded wire that circumscribes the casing equatorially. Such azimuthal tap must, however, be electrically connected (by metal of as low resistance as possible) to one pole of the gyro power supply. This has been solved to date by guiding the azimuthal tap wire that circumscribes the equatorial ring 11 inwardly, sealing it, at one point,. into the lower shell 1 and connecting it by metal to a bottom contact 10 on the underside. FIG. 5 illustrates the terminal connection 12 between the azimuthal tap and a bushing 13 that, for reasons explained above, is to be sealed in a hermetically and absolutely gas-tight fashion to a sealing packing 14 that is also compatible, particularly with regard to its coefficient of thermal expansion.
In gyrocompasses of this type, current is fed to one pole of the gyro motor(s) via a bottom contact 10 (compare FIG. 4) or from the latter to the outside via the electrically conducting liquid. The bottom contact 10 is gilded low down on the outside to insure desired, good, non-corroding contact with the surrounding conducting liquid over the long term. To avoid thermal stress problems, the body of the bottom contact 10 is preferably selected from a material adapted to the material of the lower shell 1, (i.e., aluminum) it being the case that (as FIG. 4 reveals) it presents a much more technically demanding problem, including comparatively high production costs, to fit the lower shell 1, in turn, in an absolutely airtight fashion into a corresponding cutout in the base. It is necessary in this case to insure that the outer coating of the lower shell 1 is not interrupted or damaged at any point as leaks are otherwise unavoidable after a short time. The bottom contact 10 is rigidly joined on the inside to a flange-like support 15 into the middle of which is inserted an upwardly-projecting holder 16 as bearing support for the gyro(s).
It is clear from the above that the production costs associated with the capsule that holds the gyros are substantial for a gyrocompass of this type.
It is therefore an object of the invention to simplify the structural configuration of and the production processes for a capsule for mounting the gyro(s) of a floating gyrocompass substantially.
It is another object of the invention to achieve the above object with a configuration in which the total weight of the unit, mounted to float, comprising the capsule and gyros contained therein, corresponds exactly to known units so no other changes are necessary.
The preceding and other objects are addressed by the present invention that provides a gyrocompass. Such gyrocompass includes at least one electrically driven gyro. The gyro is mounted in a gas-tight capsule supplied from an external current source through a capsule wall. The capsule is mounted to float in an electrically conducting liquid inside a compass casing.
The capsule comprises two mutually adapted shells that are sealed to one another. Each of the shells consists of a high-strength, corrosion-resistant, electrically conductive material.
Assuming that the capsule has an essentially spherical shape (not essential), it is advantageous that the capsule be formed of a lower, essentially hemispherical, shell and an upper shell with the two shell rims fitted to one another in a mutually overlapping fashion along an equatorial strip and joined in an air-tight fashion by means of a circumferential sealing packing. Since the two shells consist, according to the invention, of a high-strength, corrosion-resistant material that is a good electric conductor, the sealing external equatorial ring of shrunk-on plastic of the prior art (technically relatively complicated to produce) can be dispensed with, as there is no longer any risk of leaks due to corrosion. The technical configuration and design of the azimuthal tap is thereby rendered extraordinarily simple. To be precise, it is now possible to employ, as azimuthal tap, an equatorial strip with an uncovered surface, preferably in the overlapping rim region of the lower shell. It is thereby possible to dispense with the bushing of the azimuthal tap (illustrated in FIG. 5) on the inside of the lower shell 1, since metal contact is insured via the material of the lower shell.
An advantage which is at least just as important from the point of view of production is that, because of the use, as bottom contact, of material which is a good electric conductor but resistant to corrosion, there is no longer any need for separate components. An uncovered region of the lower shell 1 on the underside is sufficient as the bottom contact.
The foregoing and additional features of the invention will become further apparent from the detailed description that follows. Such description is accompanied by a set of drawing figures. Numerals of the drawing figures, corresponding to those of the written description, point to the features of the invention, with like numerals referring to like features throughout both the written description and the drawing figures.